Detect number of logical CPUs (threads) on OS X, not "cores".
Let config.sh take common |repo sync| options and pass them through.

For example, -d (check out the manifest revisions, instead of trying to
rebase the current HEADs onto them) is useful when changing branches or
devices, to prevent unwanted rebases that often fail.
Merge pull request #253 from jld/mac-core-count

Detect number of logical CPUs (threads) on OS X, not "cores".
Merge pull request #254 from jld/config-sync-flags

Let config.sh take common |repo sync| options and pass them through.
Update README with two caveats for Mac builds (case-insensitive FS and linker OOM with noopt).
Fixing formatting in README.md.
Removing TODOs accidentally left in README.
Merge pull request #255 from jlebar/readme-updates

Update README with two caveats for Mac builds (case-insensitive FS and l...